Financial/nonfinancial disclosures: The author has reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

To the Editor:

I thank Dr Spanbroek and colleagues for their comments on our recent article in CHEST.1 We chose two cohorts for the study because we had the opportunity to do so and could not predict the results. In fact, as pointed out, the cohorts were quite different in composition in terms of sex predominance and age variations and showed results, consistent in both cohorts, of significant increases in plasma levels of desmosine and isodesmosine (D/I) in subjects exposed to secondhand smoke. We are not aware of data showing differences between men and women in levels of D/I in normal subjects. There may be a relation between aging and increases in D/I in plasma in normal subjects, but we have not observed such a correlation in the current data available to us or in currently published studies. Larger series of studies of normal subjects of various ages may show such a relation to age, which has been suggested in aging rats.2

None of the secondhand smoke-exposed subjects were former smokers. The active smokers in both cohorts were free of respiratory symptoms and were considered to be in normal health.

The measurements of D/I in the subjects exposed to secondhand smoke were not only an average of two analyses but were based on recoveries of known amounts of spiked samples of plasma. This greatly improved accuracy and repeatability. Subsequent analyses using the pyridinoline standard3 showed acceptable similarities when compared with our previously published measurements.

A stable deuterium isotope, which is not yet available, is the ideal internal standard. We are in the process of synthesizing this standard (Yamada et al, unpublished data, November 2011). The deuterium used in the reference cited by the respondents was made by ion exchange reaction, which is not stable during hydrolysis. As pointed out, I agree that D/I remain an interesting marker for the evaluation of elastin breakdown and have so stated in a recent publication.4

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